1. Field of the Invention
The present invention relates to a catalyst support having good electroconductivity and hydrophilicity, an anode comprising the same, and a fuel cell comprising the anode.
2. Discussion of the Related Art
A fuel cell, which is a future source of clean energy that may replace fossil energy, has high power density and high energy conversion efficiency. Since the fuel cell may be operated at an ambient temperature and may be miniaturized and hermetically sealed, it may be extensively applied to the fields of zero-emission vehicles, home power generating systems, mobile telecommunications equipment, medical equipment, military equipment, space equipment, and portable electronic devices.
Fuel cells convert energy produced through electrochemical reactions of a fuel (hydrogen or methanol solution) and an oxidizing agent (oxygen or air) into electric energy. Such fuel cells may be classified as molten carbonate electrolyte fuel cells, which operate at temperatures of 500-700° C., phosphoric acid electrolyte cells, which operate at approximately 200° C., and alkaline electrolyte fuel cells and polymer electrolyte fuel cells, which operate between room temperature and 100° C.
Polymer electrolyte fuel cells include proton exchange membrane fuel cells (PEMFCs) using hydrogen gas as a fuel and direct methanol fuel cells (DMFCs) using liquid methanol solution directly applied to the anode as a fuel.
Generally, PEMFCs using hydrogen gas as a fuel have high energy density, but handling hydrogen gas requires caution and an additional appliance, such as a fuel reformer for reforming methane, methanol, and natural gas, is required to produce the hydrogen gas.
Although DMFCs have lower energy density than PEMFCs, they are considered to be suitable as a small and general-purpose portable power source from the viewpoint of manageability and low operating temperatures, and they do not require an additional fuel reforming apparatus. The fuel cell includes an anode and a cathode, to which reactant liquid/gas are supplied, and a proton conductive membrane interposed between the anode and the cathode. At the anode, decomposed methanol produces protons and electrons. The protons move through a proton conductive membrane and meet with oxygen to produce water at the cathode. Electrons moving from the anode to the cathode produce electricity.
Currently, in PEMFCs and DMFCs, the cathode uses Pt particles dispersed in a carbon support, and the anode uses Pt—Ru particles dispersed in a carbon support. A noble metallic catalyst is typically used as the catalyst of a fuel cell having such a structure, which increases the cost. Thus, catalysts having high dispersion and high efficiency using a proper carbon support are being considered for decreasing the amount of the noble metallic catalyst used.
In order to be used as a catalyst support, carbon should have proper physical properties such as an electroconductivity, a surface functional group, a mechanical strength, a surface area, a pore size, a particle size, and a shape. When used as a catalyst support for the fuel cell, the carbon should have a high electroconductivity and have a hydrophilic surface functional group that transfers methanol solution effectively and is easily dispersed in a solvent (used) when the catalyst is synthesized.
Carbon blacks such as acetylene black, Vulcan, Ketjen black, and an activated carbon are currently used in fuel cells. Specialized carbons, such as a mesoporous carbon, a carbon fiber and a carbon nanotube, are being researched.
10-60 wt % Pt or PtRu catalysts supported by Vulcan XC 72R may be purchased on the open market, and many research institutes and companies have used them.
Lasch et al. researched the use of a metal oxide as a catalyst support [K. Lasch, G. Hayn, L. Jorissen, J. Garche, and O. Besenhardt, Journal of Power Sources, 105 (2002), pp. 305-310]. Lasch et al. described that when ruthenium oxide synthesized to particle size of 13-14 nm was used as the catalyst support, the resulting catalyst had lower catalytic activity than commercially available catalysts. In other words, since only ruthenium oxide was used as the catalyst support, its small surface area provided for ineffective catalyst distribution, thereby resulting in lower catalyst activity.
Jusys et al. researched the use of a metal oxide as a cocatalyst [Z. Jusys, T. J. Schmidt, L. Dubau, K. Lasch, L. Jorrisen, J. Garche, and R. J. Behm, Journal of Power Sources, 105 (2002), pp. 297-304]. Jusys et al. described that PtRu and metal oxide are simultaneously synthesized in form of alloy by applying the Adams method. These metal oxides were used as the cocatalyst for preventing CO poisoning. In Jusys' results, thermal treatment was required since PtRu and a metal oxide was in the form of an alloy. Vanadium, molybdenum, and tungsten oxides were researched.
Kyung-Won Park et al. researched the application of a nano-composite of ruthenium oxide-acetylene black to a fuel diffusion layer [Kyung-Won Park and Yung-Eun Sung, Journal of Power Sources, 109 (2002), pp. 439-445]. It is assumed that the nano-composite of ruthenium oxide-acetylene black is not utilized as the catalyst support, but is just used in the fuel diffusion layer.